First time user of sim cards here (yup, was a VM customer for years now). I recently activated a $30 pre-paid plan from TMobile, but unfortunately I found out the phone I bought was the wrong model after I set everything up. It was an ATT Note 4 [910a] rather than the advertised TMobile Note 4 [910T].

Can I just remove the SIM card and return the phone? I believe I remember putting the IMEI of the ATT Note 4 phone during the pre-paid steps to activate, so I'm not sure if I'm stuck with the phone. Thanks for your time.

I acquired an unlocked S3 and moved my SIM into it. Everything works fine except I had no 4G connection. Is there something I need to do to enable the data connection? Is the SIM tied to my original S3 somehow? Thank you.

As mentioned previously the account is tied to the SIM. The issue may be if you bought an unlocked device that was from another carrier it may not have/support all the T-Mobile frequencies which could be what is limiting the 4G. Does the data work at all just not 4G?

I have a few follow-up questions. Do I need to back up my apps, data and media before I switch SIM card between a SAMSUNG Galaxy Light to a pre-owned Galaxy S5? If so, how do I do it? Or is there a guide you can point me to? I need to know how to backup and restore. Many thanks for your help!